Linear induction motor primary member

ABSTRACT

A primary member in or for a linear induction motor of a kind in which at least part of the working flux passes generally transversely of the motor; the primary member has a magnetic core structure terminating in at least two transversely spaced ends, and a two-layer energising winding of which the winding conductors extend generally transversely of the primary member to pass adjacent the ends of the core structure. The winding conductors are angled where they cross the gaps between the ends so that in operation the travelling magnetic fields produced by the energising winding at the two ends are substantially in antiphase with one another.

United States Patent 1191 1111 3,746,899 Eastham 1' July 17, 1973 [5LINEAR lNDUCTlON MOTOR PRIMARY 3,497,730 2/1970 Doolittle 310/13 MEMBER3,585,423 6/1971 Bolton 310/13 Inventor: John Frederick Eastham, LongDitton, Surrey, England Assignee: Tracked Hovercraft Limited, London,England Filed: Apr. 19, 1972 Appl. No.: 245,517

Foreign Application Priority Data Apr. 29, 1971 Great Britain 12,226/71References Cited UNITED STATES PATENTS 3/1934 Parvin 310/13 X PrimaryExaminer-J. D. Miller Assistant Examinerl-l. Huberfeld Attorney-Cameron,Kerkam, Sutton. Stowell & Stowell [57] ABSTRACT A primary member in orfor a linear induction motor of a kind in which at least part of theworking flux passes generally transversely of the motor; the primarymember has a magnetic core structure terminating in at least twotransversely spaced ends, and a two-layer energising winding of whichthe winding conductors extend generally transversely of the primarymember to pass adjacent the ends of the core structure. The windingconductors are angled where they cross the gaps between the ends so thatin operation the travelling magnetic fields produced by the energisingwinding at the two ends are substantially in antiphase with one another.

12 Claims, 12 Drawing Figures .Patnted July 17, 1973 3,746,899

5 Shets-Sheet 1.

Patented m 17,1973' 3,746,899

5 Sheets-Sheet B 1' a I i Patented July 17.1973 3,746,899

5 Sheets-Sheet 5 Patented July 17, 1973 3,746,899

5 Sheets-Sheet 4 Patented July 17, 1973 5 Sheets-Shet 5 LINEAR INDUCTIONMOTOR PRIMARY MEMBER This invention relates to primary members forpolyphase, especially three-phase, linear induction motors.

A polyphase linear induction motor comprises a primary member and asecondary member arranged transversely of one another for relativelongitudinal movement therebetween. The primary member carries apolyphase energising winding and the primary and secondary members arearranged and relatively disposed so that there are provided lowreluctance paths which magnetically link the primary and secondarymembers. In operation flux driven around these magnetic paths by theenergising winding induces currents in electrically conductive materialforming at least part of the secondary member; these currents in turnreact with the flux to create longitudinally directed propulsive forcebetween the primary and secondary members. For brevity such flux ishereinafter to be referred to as working flux.

As has been described and claimed in U. S. Pat. Nos. 3,585,423 and3,628,072 and the related co-pending application Ser. No. 241,069 whichis a continuation of Ser. No. 73,107, now abandoned, to which patentsand application the readers attention is drawn for further information,at least part of the working flux may pass through the primary-secondarymagnetic circuit in low reluctance paths which are orientatedtransversely of the motor.

FIG. 6 of the above mentioned application Ser. No. 241,069 shows anarrangement in which working flux is driven around transverse lowreluctance paths by two windings each wound on a respective magneticlamination stack. The stacks extend in parallel relationship to oneanother with a gap therebetween, the two energising windings beingdisposed side-by-side with their innermost winding noses adjacent oneanother and accommodated by the gap between the stacks.

The present invention stems from the realisation that the need for theadjacent winding noses can be avoided if the two windings are combined.(It will be appreciated, however, that the invention is in no waylimited to an improvement of this particular linear induction motorprimary member.)

According to one aspect of the present invention in a linear inductionmotor primary member having a magnetic core structure adapted forenabling working flux in operation to pass generally transversely of themotor around a primary-secondary magnetic circuit, the core structure isterminated magnetically in the primary-secondary magnetic circuit attransversely spaced ends, the primary member having, for creating thesaid working flux, a polyphase energising winding comprising a pluralityof winding conductors arranged in at least one winding layer, eachwinding conductor extending generally transversely of the motor in arespective said winding layer and having a first part disposed adjacentone said end of the core structure for generating working flux thereinand having a second part spaced from the first part and disposedadjacent the other said end of the core structure for generating workingflux therein, and energising means for so energising the windingconductors from the phases of a polyphase A.C. supply that in operationthe first and second parts of the conductors separately create fields ofmagneto-motive force which travel longitudinally of the primary memberat the same speed as one another and which are at least substantially inantiphase transversely of the primary member.

Preferably the said ends of the core structure are castellated toprovide core teeth longitudinally spaced apart with winding slotstherebetween. 1n the winding slots are received the first and secondparts of the winding conductors.

The primary member may be adapted for providing part of a singleprimary-secondary magnetic circuit across the width of the motor, or itmay be adapted for providing part of two (or more) such magneticcircuits side-by-side.

According to a preferred feature of the invention the winding conductorsare arranged in two winding layers, the winding conductors of eachwinding layer having at least one of their ends connected to respectivewinding conductors of the other winding layer.

Preferably the interconnection and energisation of the conductors issuch that, in operation, current equality exists generally transverselyof the motor as between the winding layers, so that the current in eachfirst conductor part is equal (and opposite) to the current in agenerally transversely disposed second conductor part in the otherwinding layer. Alternatively, however, the interconnection andenergisation of the conductors may be such that current equality existsgenerally transversely of the motor within each winding layer consideredseparately.

The winding conductors may be such that the windings which they form(and which collectively constitute the energising windings) are wavewindings, or lap windings, or looped windings with splayed-apartterminations. The windings may have only one turn or they may bemultiturn.

Preferably the winding conductors of the two winding layers aregenerally identical, when in position the winding conductors of the twowinding layers being inverted as between the winding layers.

Advantageously the energising winding is formed by a method whichcomprises preforming the winding conductors, placing winding conductorsin position to form the first winding layer with their first and secondparts received at the bottom of the winding slots, similarly forming thesecond winding layer from further winding conductors, and then makingthe interconnections between the winding conductors of the two windinglayers.

According to a further aspect of the present invenwill now becomeapparent from the following description given, by way of example andwith reference to the accompanying diagrammatic drawings, of fourembodiments of the invention and various modifications thereof. In thedrawings:

FIG. 1 is a perspective view of part of a linear induction motor ofwhich the primary member forms the first embodiment, the primary memberbeing partly cut away to show its interior,

FIG. 2 shows one of the winding conductors forming the polyphaseenergising winding of the primary member of FIG. 1,

FIG. 3 schematically illustrates in underside plan view the arrangementof the energising winding,

FIG. 4 shows one of the windings forming the energising winding anditself formed of two of the conductors of FIG. 2,

FIG. 5 corresponds to FIG. 1 in relation to the second embodiment,

FIG. 6 corresponds to FIG. 2 in relation to the second embodiment,

FIG. 7 corresponds to FIG. 3 in relation to the third embodiment,

FIG. 8 corresponds to FIG. 2 in relation to the third embodiment,

FIG. 9 corresponds to FIG. 2 in relation to the fourth embodiment,

FIG. 10 shows a modification of the conductor of FIG. 9,

FIG. 11 is a cross-sectional end elevation showing the linear inductionmotor of FIGS. 5 and 6 in a. modification, and

FIG. 12 is a similar view of the motor of FIG. 6 of the above-mentionedapplication Ser. No. 241,069, included for the purposes of comparison.

Although not apparent from the drawings, in each of the describedembodiments the primary member is mounted generally horizontally on avehicle arranged for operation along a prepared track. The co -operatingsecondary member is elongate and extends along the track verticallybeneath the primary member in spaced relation thereto.

Referring now to FIGS. 1 to 4, the first motor has its primary member 1and secondary member 2 spaced apart for relative movement in thedirection of the arrow A.

The primary member 1 comprises two horizontally disposed stacks 3, 4 oflongitudinally orientated vertical magnetic laminations 5. The stacks 3,4 are of like rectangular cross-section and extend continuously alongthe primary member in parallel relation with a gap 6 therebetween.

Disposed above the stacks 3, 4 and extending between their outermostedges are further magnetic laminations 7. The laminations 7 arerectangular and extend continuously along the primary member;individually they liein vertical planes directed transversely of themotor.

The secondary member 2 comprises a reaction member 8 of aluminium orother electrically conductive material and, on the side of the member 8remote from the primary member, magnetic backing material formed oftransversely orientated vertical magnetic laminations 9. The laminations9 and the reaction member 8 both extend continuously along the secondarymember.

Transversely of the motor the laminations 9 are generally U-shaped. Theyare so disposed and dimensioned that the ends of their arms face towardsthe under surfaces of the stacks 3, 4 and correspond laterally thereto.

The reaction member 8 extends across the width of the motor and projectsbeyond the magnetic material of the primary and secondary members ato'verhanging portions 10. The reaction member has a plane upper surfacebut has a thickness which is greater beneath the slot 6 and at theoverhanging portions 10 than beneath the stacks 3, 4.

Returning again to the primary member 1, the undersides of the stacks 3,4 are formed regularly with core teeth 55 spaced apart by transversewinding slots 11. Each slot 11 is aligned transversely of the motor witha slot 11 from the other stack 3 or 4. The slots 11 in combinationreceive the winding conductors of a threephase two-layer distributedwinding 12 of which the arrangement will become apparent from its methodof formation now to be described with reference to FIGS. 2 to 4.

The winding 12 is made up from identical, insulated winding conductors13 which may or may not be of a stranded conductor construction as shownand which are preformed generally in the form of an S, as is shown inFIG. 2 which shows one such conductor.

Each conductor 13 is generally planar and has two straight and offsetbut parallel portions 14 joined by an inclined crossover portion 15.Beyond the portions 14 the conductor has two further portions 16 whichare inclined oppositely to the crossover portion 15 and lead toconductor end portions 17 which are aligned with one another and withthe centre of the crossover portion 15.

The amount by which the parallel portions 14 are offset from one anothercorresponds to five slot pitches of the slots 11. In addition, theseparation of the portions 14 in their longitudinal direction isslightly smaller than the width of the gap 6, and the length of eachportion 14 is slightly greater than the width of each stack 3, 4. Eachconductor 13, either as shown in FIG. 2 or upside down, can therefore bepositioned on the primary member magnetic material with its portions 14received in winding slots 11 of the stacks 3, 4, which are offset byfive slot pitches.

In order to form the winding 12, identically arranged conductors 13 arepresented to the primary member magnetic material, one over each windingslot 11, and then pushed to the bottom of the slots to form the windinglayer which will be remote from the secondary member 2 in operation. Theconductors 13 forming this winding layer are indicated in FIG. 3 by thebroken lines.

The second winding layer is then formed in a similar way, but withconductors 13 which are upside down in relation to those of the firstlayer. The conductors 13 of this second layer are indicated in FIG. 3 bythe full lines.

Along the righthand side of the primary member (as seen in FIG. 3) theends of the winding conductors of one winding layer are connected to therespective adjacent ends of the winding conductors of the other layer,to form winding noses as indicated in FIG. 1 by the reference numeral18. These winding noses lie generally in planes which are orthogonal tothe winding layers, and it may be necessary or desirable to form theconductors 13 initially with the bends required for the winding noses.

The connections made at the winding noses 18 form the conductors 13 intoseparate but overlapping windings each generally in the form of a figureof eight. These windings, of which one is shown in FIG; 4 and indicatedby the reference numeral 19, are thereafter connected at their lefthandends to the phases of a three-phase A.C. supply with the pairs ofterminal ends of successive windings 19 connected to the red (R), yellow(Y) and blue (B) phases of the supply in the following cyclical order:R, R, T, T, B, B, F, i, Y, Y, E, T3, R, etc., the bars above the phaseletters denoting that the connection to the appropriate phase of thesupply is reversed.

It will also be appreciated that at some stage after the windingconductors 13 have been placed in position they will be secured in thewinding slots 11 by, for example, slots wedges and/or a thermosettingresin.

In operation, when the primary member is disposed in spaced relation tothe secondary member as shown in FIG. I, the energisation of thewindings 19 as described above causes each stack 3, 4 to generate, inknown manner, a resultant field of magnetomotive which travelslongitudinally of the primary member; the resultant fields produced bythe two stacks travel in the same direction and at equal speedsdependent upon the pitch of the slots 11 and the frequency of the A.C.supply.

The pitching of the winding conductors in each of the two layers and theoffsetting of the conductors between the stacks is such that the twocurrents flowing in each winding slot are equal and opposite torespective ones of the two currents flowing in the corresponding, i.e.,transversely aligned, winding slot. Thus the resultant travellingmagnetomotive forces produced by the stacks 3, 4 are antiphase, andthese two fields additively combine to drive flux around parallel andtransversely orientated low reluctance paths comprising in series, thelaminations of the stack 3, the transverse laminations 7, thelaminations 5 of the stack 4, and then the laminations 9 of thesecondary member and back to the primary member at the laminations ofthe stack 3.

As is illustrated in FIG. 1 by the broken line 20, flux passing in thesetransverse magnetic paths passes twice through the reaction member 8,once beneath the stack 3 and once beneath the stack 4. In so doing itinduces in the reaction member currents which flow in generallyrectangular paths corresponding to the magnetic poles set up by eachstack. In known manner, the parts of the currents beneath the stacks 3and 4, orientated generally transversely of the motor, react with theflux to produce propulsive force in the direction of the arrow A in FIG.1.

The thickened part of the reaction plate, i.e., at the overhangingportions and beneath the slots 6, provides low resistance paths for thelongitudinally extending parts of the secondary member current paths, sothat current flow in the reaction member 8 beneath the stacks 3 and 4can be substantially transverse of the motor and therefore fullyeffective to produce propulsive force.

In addition to the flux paths as described above, some working fluxassociated with each stack 3, 4 separately will also pass longitudinallyof the motor in flux paths provided in part by the laminations 5 intheir longitudinal direction. One such flux path is indicated in FIG. 1by the broken line 21. The parts of the laminations 5 bridging thewinding slots 11 are dimensioned to saturate at a low level of flux and,in addition, the longitudinal flux paths are transverse to thelaminations 9 and therefore of relatively high A.C. reluctance, that isto say, the reluctance taking into account the effects of eddy currentsassociated with the paths; the contribution of the flux passing in theselongitudinally directed paths to the total propulsive force willtherefore be small. One of the many reasons for providing thelongitudinal laminations 5 is to enable the winding slots 11 easily tobe made partially closed and to give the primary member mechanicalstrength in the longitudinal direction.

In the embodiment of FIGS. 1 to 4 the windings l9 span five slot pitchesin each stack 3, 4 and are so energised that for each stack thetravelling fields separately produced by the two winding layers aredisplaced from one another by 30 (elect); in non-illustratedmodifications of the first embodiment the windings l9 span four, six,seven and eight slot pitches so that, with the same energisation of thewindings as previously described, the phase displacement is respectively60 (elect) in the same sense as the first embodiment, zero, and 30(elect) and 60 (elect) in the opposite sense.

A feature of the arrangement of FIGS. 1 to 4 and of the non-illustratedmodifications of the last paragraph is that in aligned winding slots thedirectly antiphase currents occur in different winding layers. However,current equality in aligned winding slots can, if desired, be providedin the same winding layer, but this not only requires the crossoverportions 15 of the winding conductors to span a whole pole pitch of theapplied electrical supply, but also unless in each winding slot thecurrents in the two conductors are the same (i.e., zero phasedisplacement), it also requires different lengths for the furtherportions 16 along the two sides of the motor.

In a modification of such an arrangement only one of the layers ofwinding conductors is provided, the other layer being omitted. Thewinding conductors forming the single winding layer remaining aresuitably connected to the energising A.C. supply.

Thus transverse current equality in the winding layers taken separatelywill normally require conductors with relatively long crossover portions15 and unequal further portions 16. Generally speaking, therefore,transverse current equality as between winding layers will be preferred.

In one possible arrangement having transverse current equality in thewinding layers taken separately and having the energisation previouslydescribed, each' component winding (such as the winding 19 of FIG. 4)has one loop spanning five slot pitches and the other loop spanningseven slot pitches. This gives a phase displacement of 30 (elect)between the two currents in each winding slot. Likewise, for a 60(elect) phase displacement one loop spans four slot pitches and theother loop eight.

In the arrangement of FIGS. 1 to 4 and the modifications thereof onlyone transverse low reluctance path for working flux is provided acrossthe width of the motor; however, it will be appreciated that a primarymember in accordance with the invention may have two or more transverselow reluctance paths provided across its width, and FIGS. 5 and 6 show afurther embodiment in which two low reluctance paths are providedside-by-side.'

Referring now to FIG. 5, the primary member 22 of the second embodimentcomprises transversely orientated magnetic laminations 23 backing threestacks of longitudinal laminations 24 spaced apart by longitudinal gaps25, the centre stack 26 being approximately twice as wide as the outerstacks 27.

The secondary member 28 comprises a reaction member 29 which is backedby generally W-shaped transverse laminations 30 and is thickened atoverhanging portions 31 and at the portions 41 beneath the gaps 25.

At their undersurfaces the stacks 26, 27 are regularly formed with coreteeth 56 spaced apart by transversely aligned winding slots 32. In theslots 32 is located a double layer, distributed, three-phase A.C.winding 33.

The winding 33 is made up from generally planar winding conductors 34(see FIG. 6) by exactly the same method of assembly as previouslydescribed in relation to the first embodiment. In FIG. 6 portions of thewinding conductors 34 which are received in the winding slots 32 areindicated by the reference numeral 35, the crossover portions bridgingthe winding slots by the reference numeral 36, the inclined portionsflanking the outer ones of the portions 35 by the reference numeral 37,and the conductor end portions by the reference numeral 38.

In a corresponding way to the first embodiment, the offsetting of thecentral portion 35 of each winding conductor from the outer portions 35thereof is by five slot pitches, and the terminal ends 38 are co-linearwith the centres of the crossover portions 36.

For operation the individual windings formed by the interconnection ofthe winding conductors 34 at the winding noses 39 are connected to thephases of a three-phase A.C. supply as previously described in relationto the first embodiment, and it will be appreciated that, because theresultant travelling fields produced by the outer stacks 27 are in phasewith one another and in antiphase to the resultant field produced by thecentre stack 26, working flux will pass transversely of the motor inside-by-side pairs of flux paths as is illustrated in FIG. by the brokenlines 40.

It will also be appreciated that, as in the first embodiment, a smallamount of longitudinally directed flux will be associated with eachstack 26, 27 separately.

The embodiment of FIGS. 5 and 6 can be considered to be formed of two ofthe motors of FIGS. 1 to 4 arranged side-by-side with the adjacent partsof their transverse magnetic paths provided in common by the centrestack 26, and further non-illustrated embodiments are formed by theanalogous combination of pairs of motors of the described modificationsof the first embodiment.

Although the invention has so far been described in relation to what maybe considered to be lap windings, i.e., windings which are almostclosed, other types of winding may also be used. One such arrangement,illustrated in FIGS. 7 and 8, is a wave-wound version of the firstembodiment, being identical to it in all but the arrangements of thethree-phase winding.

Referring now to FIGS. 7 and 8, the three-phase winding 42 of this thirdembodiment is made up from generally planar winding conductors 43 ofwhich one is shown in FIG. 8. Like the winding conductors 13 of thefirst embodiment, each conductor 43 has two straight and offset butparallel portions 44 joined by an inclined crossover portion 45 andflanked by further inclined portions 46 extending to the conductor endportions 47. Whereas in the first embodiment the portions 16 areoppositely inclined to the crossover portions IS, in this thirdembodiment the portions 45 and 46 have the same direction ofinclination.

In each conductor 43 the offsetting of the portions 44 corresponds tofive slot pitches of the winding slots 11, and the length andinclination of the further portions 46 is such that the conductor endportions 47 are offset by three and a half slot pitches from theadjacent ones of the portions 44.

The method of assembly of the conductors 43 to form the three-phasewinding 42 is the same as the formation of the windings of the previoustwo embodiments and results in separate but overlapping wave windings 48having winding noses 49 at their right hand sides. The connection ofthese wave windings 48 for energisation from a three-phase supply isalso the same as previously described in relation to the firstembodiment. Thus successive windings 48 are connected to the three-phaseof the supply in the cyclic order: R, R, Y, Y, B, B, R, R, Y, Y, F, F, Retc. It will be seen that the currents in the winding conductors in eachwinding slot are equal and opposite to those in the winding conductorsin the corresponding winding slot of the other lamination stack.

The arrangement of the fourth embodiment of the invention is evidentfrom FIG. 9 which shows one of the generally planar winding conductors50 from which the three-phase winding is formed by the procedurepreviously described. The fourth embodiment has the same magneticstructure and reaction member as the second embodiment and can beconsidered to be a wavewound version of the second embodiment (FIGS. 5and 6), being such as to provide two transverse low reluctanee paths forworking flux side-by-side across the width of the motor.

In FIG. 9 those parts of the winding conductor 50 which are received inthe winding slots are indicated by the reference numeral 51, thecrossover portions bridging the winding slots by the reference numeral52, the inclined portions flanking the outer ones of the portions 51 bythe reference numeral 53, and the conductor end portions by thereference numeral 54.

The offsetting of the portions 51 from one another is by five slotpitches, and the offsetting of each conductor end portion 54 from theneighbouring portion 51 is by three and a half slot pitches.Energisation of the winding formed from the conductors 50 is exactly aspreviously described, with the result that, like the second embodiment,laterally of the motor the outer lamination stacks produce travellingfields of magnetomotive force which are in antiphase with the fieldproduced by the centre stack, so that working flux is driven around theside-by-side flux paths in the manner indicated in FIG. 5.

As in the previous embodiments, some working flux will passlongitudinally of the motor through flux paths separately provided inpart by the stacks 26, 27 in their longitudinal direction.

In a modification of the fourth embodiment, the portion 53 at the righthand end of each winding conductor 50 is inclined in the oppositedirection to that shown and reduced in length so that the respectiveconductor end portion 54 is offset from the right hand portion 51 by twoand a half slot pitches. The separate but overlapping windings formingthe three-phase winding are then as shown in FIG. 10.

Although the described embodiments of the invention have their windingsformed of winding conductors which are generally planar for location intwo or more laterally spaced but coplanar winding slots, this is notessential. For example, FIG. I] shows a modification of the secondembodiment in which the laminations 23 are generally U-shaped, so thattransversely of the motor the primary member comprises two parallel armswith a central portion extending orthogonally therebetween. The outerlamination stacks 27 are carried at the inside faces of the arm ends soas to oppose one another; the central stack 26 is centrally carried bythe central portion.

The reaction member 8 has a generally U-shaped configuration so as tocorrespond to the general configuration of the primary member. Thesecondary member thus has three orthogonal outer faces which, in use,oppose respective ones of the lamination stacks 26, 27.

The three-phase winding located in the winding slots on the faces of thestacks 26, 27 is formed of winding conductors which are bent throughslightly more than 90 degrees at their crossover portions 36 and so aregenerally U-shaped in side elevation.

The method of assembling the three-phase winding from three conductorsis essentially as previously de-- scribed except that the portions 35 tobe received in the winding slots of the outer stacks 27 are bentoutwardly into position when the centre portions 35 have been located.

Although each of the described embodiments has each of its laminationstacks 3, 4, 26, 27 opposed by a corresponding part of the co-operatingreaction member so that each stack has associated secondary membercurrent paths, such an arrangement is not essential. In modifications ofthe first and third embodiments the reaction member opposes only one ofthe stacks 3 and 4, being stopped just short of the outer stack;likewise, in modifications of the second and fourth embodiments thereaction member opposes only the centre stack 26, stopping just short ofthe outer stacks 27 on either side. In each such modification the partor parts of the secondary member magnetic material directly opposing therespective stack 3, 4 or stacks 27 are made flush with the upper surfaceof the reaction member.

In a modification of each of the described embodiments the transverselaminations 7, 23 are provided only in correspondence with the coreteeth 55, 56; they then form discrete, longitudinally spaced laminationstacks.

In a further modification the stacks of longitudinally orientatedlaminations are replaced by planar extensions of the transverselaminations. In an arrangement in accordance with the precedingparagraph the winding slots will then be provided by the gaps betweenadjacent stacks of transverse laminations. In an arrangement such asthose shown in the drawings having its transverse laminations continuousalong the motor, the winding slots may be formed either by the use ofappropriately dimensioned laminations or after assembly by, for example,a milling operation. It will be appreciated that in such an arrangementsubstantially all the working flux will pass transversely, orsubstantially transversely, of the motor.

If desired the lamination stacks of the described embodiments may beindividually replaced by one or more solid blocks of magnetic material;in addition, the parts of the longitudinal laminations or solid blocksbridging the winding slots may be ofa sufficient depth not to saturate.

In each of the described embodiments the ends of the primary member partof each motor primary-secondary magnetic circuit are formed with coreteeth separated longitudinally of the primary member by winding slots inwhich are received the winding conductors. In yet another possiblemodification, however, the core teeth are omitted, the lower faces ofthe stacks 3, 4 or 26, 27 being planar instead of castellated. Thewinding conductors are secured against these planar faces by suitableclamping devices and/or by thermosetting resin.

As previously described in relation to the first embodiment, in aprimary member in accordance with the invention transverse currentequality may exist either in the winding layers taken separately or asbetween winding layers. This is dependent, of course, upon theparticular energisation of the component windings from a polyphasesupply and upon the winding conductors and their interconnection.

The pole pitch of the travelling magnetic field produced by eachlamination stack depends, of course, upon the winding energisation used,and may be varied as desired.

Although the described embodiments have an integral number of windingslots per pole per phase a nonintegral number may be used if desired. 0e nonillustrated embodiment of this kind has its energising windingformed of windings of the kind shown in FIG. 4 and having each loopspanning four slot pitches; for operation the windings are successivelyenergised from the red (R), yellow (Y) and blue (B) phases of athreephase supply in the order: R, T, B, B, Ii, Y, Y, 13, R, R, Y, B, RY, l3, R etc.

Each of the described embodiments and modifications thereof is such thateach of the two current in one winding slot is equal and opposite to arespective one of the currents in a transversely aligned winding slot ofat least one other stack; thus the resultant travelling fields producedby the respective stacks are equal in magnitude and directly inantiphase transversely of the motor. It is not essential, however, thatthe resultant fields produced by the two stacks should be in exactantiphase and equal so that current equality transversely of the motorneed not necessarily apply.

If desired a primary member in accordance with the invention maycomprise two or more polyphase windings such as have been described,superimposed upon one another.

Although in the described embodiments the individual windings formingeach energising winding each have only one turn, it will be appreciatedthat multiturn windings may be used. Thus in the first and secondembodiments the pairs of conductors 13, 34 forming the individual lapwindings may be connected together with their strands in series orseries-parallel rather than in parallel as described.

The present invention provides a linear induction motor primary memberhaving one or more polyphase energising windings which are two-layersand distributed and which, despite being arranged to generate at leasttwo transversely spaced and generally anti-phase travelling fields ofmagnetomotive force, require the same number of winding connections tobe made as if they were separately required to produce only onetravelling field. Not only is the formation of the or each windingsimplified, but also the absence of winding noses between the parts ofthe winding separately effective to create travelling magnetic fieldstends to reduce the spacing required between those winding parts whendisposed side-by-side. Thus the invention enables a single-sided linearinduction motor having generally flat primary and secondary members tobe made narrower than might otherwise be possible, this being ofparticular value where, as described the motor is used to propel avehicle along a prepared track which includes the secondary member ingenerally horizontal disposition.

FIG. 12 is a view corresponding to FIG. 1 showing a primary member ofthe first embodiment with the stacks 3, 4 separately formed withthree-phase windings of the conventional two-layer type, as is describedwith reference to FIG. 6 of the previously mentioned application Ser.No. 241,069. From a comparion of FIGS. 1 and 12 of the presentapplication the above features can be clearly appreciated. Otherfeatures of the windings of the described embodiments of the presentinvention are the comparative ease with which the crossover portions canbe secured against movement and the comparative ease of cooling.

The invention is not limited to single-sided linear induction motors ashave particularly been described, but may also be applied todouble-sided linear induction motors (in which the primary member hastwo parts disposed one on either side of the secondary member). Thus, inaccordance with the present invention are double-sided primary memberseach comprising two of the primary members of a respective one of thedescribed embodiments connected together in spaced relation. Inoperation each such double-sided primary member is arranged to straddlean electrically conductive, plate-like secondary member, and theenergising windings of its two parts are energised in oppposed senses sothat the corresponding lamination stacks 3 or 4, or 26 or 27 (asappropriate) generate magnetomotive forces which are additive andtherefore combine to drive working flux through the interposed secondarymember.

A further double-sided primary member in accordance with the inventionis formed of the primary member of FIGS. 1 to 4 or FIGS. 7 and 8 when,as it were, bent into the shape ofa hairpin (in cross-section) with thestacks 3, 4 opposing one another in parallel relation along theirlengths.

As previously mentioned in relation to the first embodiment, theinvention is not restricted to doublelayer energising windings butincludes within its scope linear induction motor primary members (andmotors including such primary members) having one or more single-layerwindings. In such an arrangement the offsetting of the two parts of eachwinding conductor associated with each primary-secondary magneticcircuit will be by substantially one pole pitch of the travellingmagnetic field.

I claim: a

l. A linear induction motor primary member having a magnetic corestructure adapted for enabling working flux in operation to passgenerally transversely of the motor around a primary-secondary magneticcircuit, wherein the core structure is terminated magnetically in theprimary-secondary magnetic circuit at transversely spaced ends, theprimary member having, for creating the said working flux, a polyphaseenergising winding comprising a plurality of winding conductors arrangedin at least one winding layer, each winding conductor extendinggenerally transversely of the motor in a respective winding layer andhaving a first part disposed adjacent one said end of the core structurefor generating working flux therein and having a second part spaced fromthe first part and disposed adjacent the other said end of the corestructure for generating working flux therein, and energising means forso energising the winding conductors from the phases of a polyphase A.C.supply that in operation the first and second parts of the windingconductors separately create fields of magnetomotive force which travellongitudinally of the primary member at the same speed as one anotherand which are at least sustantially in antiphase transversely of theprimary member.

2. A primary member according to claim 1, wherein the winding conductorsare arranged in two winding layers, the winding conductors of eachwinding layer having at least one of their ends connected to respectivewinding conductors of the other winding layer.

3. A primary member according to claim 1, wherein each said end of themagnetic core structure is formed with core teeth spaced longitudinallyof the primary member with winding slots therebetween, the first andsecond parts of the winding conductors being received in said windingslots of respective ones of the said core structure ends.

4. A primary member according to claim 1, wherein the magnetic corestructure is adapted for providing part of a single primary-secondarymagnetic circuit across the width of the motor.

5. A primary member according to claim 4, wherein the magnetic corestructure comprises two first magnetic structures extendinglongitudinally of the primary member in parallel spaced relationship andeach providing one said end of the core structure, and a second magneticstructure extending between the first magnetic structure remote from thetwo said ends of the core structure so as magnetically to bridge thespace between the two first structures.

6. A primary member according to claim 5, wherein each first magneticstructure comprises a plurality of magnetic laminations each orientatedlongitudinally of the primary member and disposed edge-on to therespective said end of the core structure, and the said second magneticstructure comprises a plurality of magnetic laminations each orientatedtransversely of the primary member.

7. A primary member according to claim 1, wherein the magnetic corestructure is adapted for providing part of two primary-secondarymagnetic circuits sideby-side across the width of the motor.

8. A primary member according to claim 1, wherein the individualwindings and the energising means are so arranged and interconnectedthat in operation the first part of each winding conductor carries acurrent which is equal and opposite to the current in the second part ofa respective winding conductor of the other winding layer, the saidfirst part and the said second part being substantially alignedtransversely of the primary member.

9. A primary member according to claim I, wherein the winding conductorsare identical, the winding conductors of the two winding layers beinginverted as between the winding layers.

10. A linear induction motor having a primary member and a secondarymember arranged transversely of one another for relative longitudinalmovement therebetween, said primary member comprising a magnetic corestructure and an energising winding associated therewith, said secondarymember comprising electrically conductive material, said primary andsecondary members being arranged in combination to provide aprimary-secondary magnetic circuit for working flux created by saidenergising winding to pass generally transversely of the motor, saidprimary member core structure being terminated magnetically in theprimarysecondary magnetic circuit at transversely spaced ends, theenergising winding comprising a plurality of winding conductors arrangedin at least one winding layer, each winding conductor extendinggenerally transversely of the motor in a respective said winding layerand having a first part disposed adjacent one said end of the corestructure for generating working flux therein and having a second partspaced from the first part and disposed adjacent the other said end ofthe core structure for generating working flux therein, and energisingmeans for so energising the winding conductors from the phases of apolyphase A.C. supply that in operation the first and second parts ofthe conductors separately create fields of magnetomotive force whichtravel longitudinally of the primary member at the same speed as oneanother and which are at least substantially in antiphase transverselyof the primary member.

11. A linear induction motor having a primary member and a secondarymember arranged transversely of one another for relative longitudinalmovement therebetween, said primary member comprising a magnetic corestructure and an energising winding associated therewith, said secondarymember compoising electrically conductive material, said primary andsecondary members being arranged in combination to provide aprimary-secondary magnetic circuit for working flux created by saidenergising winding to pass generally transversely of the motor, saidprimary member core structure being terminated magnetically in theprimarysecondary magnetic circuit at transversely spaced ends, theenergising winding comprising a plurality of winding conductors arrangedin two winding layers, each winding conductor extending generallytransversely of the motor in a respective said winding layer and havinga first part disposed adjacent one said end of the core structure forgenerating working flux therein and having a second part spaced from thefirst part and disposed adjacent the other said end of the corestructure for generating working flux therein, the winding conductors ofone winding layer having at least one of their ends connected torespective winding conductors of the other winding layer, and energisingmeans for so energising the winding conductors from the phases of apolyphase A.C. supply that in operation the first and second parts ofthe winding conductors separately create fields of magnetomotive forcewhich travel longitudinally of the primary member at the same speed asone another and which are at least substantially in antiphasetransversely of the primary member.

12. A linear induction motor primary member having a magnetic corestructure adapted for enabling working flux in operation to passgenerally transversely of the motor around a primary-secondary magneticcircuit, wherein the core structure is terminated magnetically in theprimary-secondary magnetic circuit at transversely spaced ends, theprimary member having, for creating the said working flux, a polyphaseenergising winding comprising a plurality of winding conductors arrangedin two winding layers, each winding conductor extending generallytransversely of the motor in a respective said winding layer and havinga first part disposed adjacent one said end of the core structure forgenerating working flux therein and having a second part spaced from thefirst part and disposed adjacent the other said end of the corestructure for generating working flux therein, the winding conductors ofone winding layer having at least one of their ends connected torespective winding conductors of the other winding layer, and energisingmeans for so energising the winding conductors from the phases of apolyphase A.C. supply that in operation the first and second parts ofthe conductors separately create fields of magnetomotive force whichtravel longitudinally of the primary member at the same speed as oneanother and which are at least substantially in antiphase transverselyof the,

primary member.

* III

1. A linear induction motor primary member having a magnetic core structure adapted for enabling working flux in operation to pass generally transversely of the motor around a primarysecondary magnetic circuit, wherein the core structure is terminated magnetically in the primary-secondary magnetic circuit at transversely spaced ends, the primary member having, for creating the said working flux, a polyphase energising winding comprising a plurality of winding conductors arranged in at least one winding layer, each winding conductor extending generally transversely of the motor in a respective winding layer and having a first part disposed adjacent one said end of the core structure for generating working flux therein and having a second part spaced from the first part and disposed adjacent the other said end of the core structure for generating working flux therein, and energising means for so energising the winding conductors from the phases of a polyphase A.C. supply that in operation the first and second parts of the winding conductors separately create fields of magnetomotive force which travel longitudinally of the primary member at the same speed as one another and which are at least sustantially in antiphase transversely of the primary member.
 2. A primary member according to claim 1, wherein the winding conductors are arranged in two winding layers, the winding conductors of each winding layer having at least one of their ends connected to respective winding conductors of the other winding layer.
 3. A primary member according to claim 1, wherein each said end of the magnetic core structure is formed with core teeth spaced longitudinally of the primary member with winding slots therebetween, the first and second parts of the winding conductors being received in said winding slots of respective ones of the said core structure ends.
 4. A primary member according to claim 1, wherein the magnetic core structure is adapted for providing part of a single primary-secondary magnetic circuit across the width of the motor.
 5. A primary member according to claim 4, wherein the magnetic core structure comprises two first magnetic structures extending longitudinally of the primary member in parallel spaced relationship and each providing one said end of the core structure, and a second magnetic structure extending between the first magnetic structure remote from the two said ends of the core structure so as magnetically to bridge the space between the two first structures.
 6. A primary member according to claim 5, wherein each first magnetic structure comprises a plurAlity of magnetic laminations each orientated longitudinally of the primary member and disposed edge-on to the respective said end of the core structure, and the said second magnetic structure comprises a plurality of magnetic laminations each orientated transversely of the primary member.
 7. A primary member according to claim 1, wherein the magnetic core structure is adapted for providing part of two primary-secondary magnetic circuits side-by-side across the width of the motor.
 8. A primary member according to claim 1, wherein the individual windings and the energising means are so arranged and interconnected that in operation the first part of each winding conductor carries a current which is equal and opposite to the current in the second part of a respective winding conductor of the other winding layer, the said first part and the said second part being substantially aligned transversely of the primary member.
 9. A primary member according to claim 1, wherein the winding conductors are identical, the winding conductors of the two winding layers being inverted as between the winding layers.
 10. A linear induction motor having a primary member and a secondary member arranged transversely of one another for relative longitudinal movement therebetween, said primary member comprising a magnetic core structure and an energising winding associated therewith, said secondary member comprising electrically conductive material, said primary and secondary members being arranged in combination to provide a primary-secondary magnetic circuit for working flux created by said energising winding to pass generally transversely of the motor, said primary member core structure being terminated magnetically in the primary-secondary magnetic circuit at transversely spaced ends, the energising winding comprising a plurality of winding conductors arranged in at least one winding layer, each winding conductor extending generally transversely of the motor in a respective said winding layer and having a first part disposed adjacent one said end of the core structure for generating working flux therein and having a second part spaced from the first part and disposed adjacent the other said end of the core structure for generating working flux therein, and energising means for so energising the winding conductors from the phases of a polyphase A.C. supply that in operation the first and second parts of the conductors separately create fields of magnetomotive force which travel longitudinally of the primary member at the same speed as one another and which are at least substantially in antiphase transversely of the primary member.
 11. A linear induction motor having a primary member and a secondary member arranged transversely of one another for relative longitudinal movement therebetween, said primary member comprising a magnetic core structure and an energising winding associated therewith, said secondary member compoising electrically conductive material, said primary and secondary members being arranged in combination to provide a primary-secondary magnetic circuit for working flux created by said energising winding to pass generally transversely of the motor, said primary member core structure being terminated magnetically in the primary-secondary magnetic circuit at transversely spaced ends, the energising winding comprising a plurality of winding conductors arranged in two winding layers, each winding conductor extending generally transversely of the motor in a respective said winding layer and having a first part disposed adjacent one said end of the core structure for generating working flux therein and having a second part spaced from the first part and disposed adjacent the other said end of the core structure for generating working flux therein, the winding conductors of one winding layer having at least one of their ends connected to respective winding conductors of the other winding layer, and energising means for so energising the winding conductors from the phases oF a polyphase A.C. supply that in operation the first and second parts of the winding conductors separately create fields of magnetomotive force which travel longitudinally of the primary member at the same speed as one another and which are at least substantially in antiphase transversely of the primary member.
 12. A linear induction motor primary member having a magnetic core structure adapted for enabling working flux in operation to pass generally transversely of the motor around a primary-secondary magnetic circuit, wherein the core structure is terminated magnetically in the primary-secondary magnetic circuit at transversely spaced ends, the primary member having, for creating the said working flux, a polyphase energising winding comprising a plurality of winding conductors arranged in two winding layers, each winding conductor extending generally transversely of the motor in a respective said winding layer and having a first part disposed adjacent one said end of the core structure for generating working flux therein and having a second part spaced from the first part and disposed adjacent the other said end of the core structure for generating working flux therein, the winding conductors of one winding layer having at least one of their ends connected to respective winding conductors of the other winding layer, and energising means for so energising the winding conductors from the phases of a polyphase A.C. supply that in operation the first and second parts of the conductors separately create fields of magnetomotive force which travel longitudinally of the primary member at the same speed as one another and which are at least substantially in antiphase transversely of the primary member. 